Selector switch



July 12, 1938. w. w. CARPENTER ET AL 2,123,229

SELECTOR SWITCH Filed March 31, 19357 4 Sheets-Sheet l -W.W.CARPENTER MENTOR RFMALL/NA A T TORNE V July 12, 1938. w. w. CARPEINTER ET AL 2,1 3,229

SELECTOR SWITCH Filed 'MarchSl, 1937 4 Sheets-Sheet 2 FIG. 2

1 MWcARPENrER 'REMALZ/NA Q P 53 QaM A T TORNEV July 12, 1938. w. w. CARPENTER El AL 2,123,229

SELECTOR SWITCH Filed March 31, 1957 4 Sheets-Sheet 3 F/G. H 26 24 .yrv 62 I fill! i "ilHjjlH 53 I" 72 74 75 Q l 23 P. FMALL/NA BY ATTORNEY y 2, 1938. w. w. CARPENTER ET AL 9 39 SELECTOR SWITCH Filed March 31, 1937 4 Sheets-Sheet 4 Q W. WCARPENTE/P WVENTORS; RFMALL/NA a a ATTORNEY Patented July 12, 1938 UNITED STATES PATENT OFFICE? SELECTOR SWITCH Telephone Laboratories, York, N. Y., a corporation Incorporated, New

of New York Application March 31, 1937, Serial No. 133,970

18 Claims.

This invention relates to selector switches applicable for use in machine switching telephone systems and more particularly to switches of the terminal hunting type having access to large groups of line or trunk terminals.

In machine switching telephone systems selector switches either of the step-by-step or power driven panel type are used extensively as line or trunk finders and in some systems as trunk finders at selection stages under the control of controllers or markers. Heretofore such switches have been limited in their speed of operation by their inherent physical characteristics; in the case of step-by-step type switches, by the speed at which the stepping mechanism can be operated without undue wear and vibration and in the case of power driven switches of the well-known panel type, by the speed at which the brushes may be stopped and accurately centered by the commutator on the desired bank terminal.

For example, the panel type line finder, now widely used, employs ten sets of brushes mounted on a single elevator rod, the ten brush sets having access to ten banks of terminals in which subscribers lines terminate. With this construction it is necessary that the distances between the brush sets on the elevator rod and the distances between terminals in the bank be in accurate relationship thus increasing the cost of manu fact-ure and assembly. Each line finder is also equipped with a stationary commutator with which brushes mounted on the elevator rod engage for making electrical connections between the brush sets and outside wiring and for controlling the stopping of the hunting movement of the switch when one of the brush sets engages the terminals of a calling line. Since the accurate centering of a brush set upon the terminals of a calling line is dependent upon the commutator, it is therefore essential that the commutator be constructed and assembled .on the switch with its segments in accurate relationship with the terminals of the bank. Furthermore, since the total mass of the switch to be accelerated and de-accelerated comprises the elevator rod, the ten brush sets, the commutator brushes and the wiring between the brush sets and the commutator brushes, the energy necessary for starting and stopping the movement of the switch is such that the hunting speed must be kept low, or at approximately forty terminals per second. It is customary to mount the ten panel banks upon a single frame and to assemble thirty elevators on the frame on each side of the double-faced bank. A unit of this type is too large and heavy for shipment as an entirety and therefore it is necessary to partially disassemble the frame before shipment and to reassemble it at the place of installation thus further adding to the cost.

Since the central oflice equipment for machine switching systems is expensive, it is particularly essential therefore that it be used with the utmost eificiency. If equipment is slow in operation, a larger amount of equipment must be installed to handle peak loads than would be the case if equipment of. a faster operating type were available thus increasing the first cost of installation and increasing the carrying charges and cost of maintenance. Furthermore, it is essential that connections shall be established between subscribers lines and central office equipment as speedily as possible to guard against the possibility of wrong connections should subscribers start dialing within a short interval after the removal of their receivers from the switchhooks.

It is therefore the object of the present invention to provide a switch of the hunting type which may be driven at a high terminal hunting speed, which has small mass to be accelerated and deaccelerated whereby small energy is required for its operation, which makes provision for the accurate centering of a brush set on a set of bank terminals which has been placed in a calling condition without the use of a centering commutator, and which is economical to manufacture and assemble. A further object of the invention is to provide a switch which may be used in any type of machine switching system where line finders, trunk finders or marker controlled selectors of the hunting type may be employed.

In accordance with the present invention these objects are attained by providing a line finder frame capable of accommodating the customary sixty finder switch units. Two panel banks of the same general type as are commonly used on the well-known panel type switch frames are mounted vertically thereon side by side, each bank being provided with one hundred sets or" vertically disposed multiple terminal strips, each set having multiples for accessibility from thirty finder switch units on each side of the bank. By the provision of the two banks of one hundred terminal sets each, two hundred lines, trunks or links may be terminated thereon.

Mounted horizontally on each side of the switch frame in front of the thirty horizontal rows of two hundred terminal sets of the two banks are thirty finder switch units. Each switch unit comprises a single brush set of three end in a commutator therewith is a channel member also secured at its opposite ends to the brackets and having within its channel as many commutator strips as there are brush springs in the brush set, the commutator strips being suitably insulated from each other and from the channel member. By the engagement of the commutator brushes of the brush springs with thesecommutator strips, electrical connection to the brush springs may be made irrespectiveof the position of the brush carriage along its supporting guide rod.

The brush carriage is traversed along the guide rod in either direction by a steel tape which runs over two pulleys or flanged drums mounted for rotation on spindles secured to the two brackets. The ends of the tape are secured to the brush carriage by coiled springs which serve to tension the tape and to act as shock absorbers when the movement of the tape is abruptly arrested. One pulley is an idler and the other is a driving pulley which may be rotated in either a clockwise or counter-clockwise direction through suitable gearing by an individual reversible alternating current motor, the gearing and motor being supported by the same bracket as the driving pulley.

To insure a quick stopping of the tape and brush carriage attached thereto, a magnetically releasable brake is provided. The brake includes two cooperating brake shoes, one on either side of a traverse of the tape, one being fixed and the other secured to the armature of. the brake magnet. The brake mechanism 'is secured to the bracket. upon which the driving pulley is journalled. The armature is normally operated by a spring to press the shoes together to embrace the tape, the leverage of the armature being such that the movement of the shoe attached thereto is very slight, but that the braking force supplied by the spring is quite large. The brake magnet winding is arranged to be operated simultaneously with the driving motor so that when the motor is operated to traverse the tape in either direction the brake magnet is energized to release the brake.

The brush carriage is normally positioned at the mid-point between the two banks and when started in either direction operates a double throw normalling switch mounted on the channel member at the mid-point thereof. This switch is instrumental for reversing the direction of rotation of the driving motor to return the brush carriage to its normal position when the connection established by the switch unit is released.

Since the moving parts of the switch unit have very little mass, the brush carriage maybe accelerated and de-accelerated rapidly and the switch is therefore capable of being operated with a very small amount of power at hunting speeds far in excess of. those heretofore attained. In fact, a hunting speed of two hundred and fifty terminals per second is easily attainable and a hunting speed up'to four hundred terminals per second is possible.

To insure that the brush set when traversed at these high hunting speeds shall be stopped and accurately centered'on a terminal set which has been marked as in a calling condition, a palareaiaae If the test brush overruns the test terminal due to the speed at which it is moving, the test relay will not have time to fully operate and, with ground then removed from the test terminal, the first condenser will become fully charged and the test relay will be operated by the charging 7 current until it decays when the relay will release. The test relay upon operating stops the movement of. the brush carriage and prepares circuits for driving it back to the marked terminal set. If the brush set has overrun the terminal set then when the test relay releases the brush carriage is driven back until the brush set again engages the set of terminals. Since the second condenser is now fully charged it ofiers a low resistance shunt around the first resistance and the test relay reoperates opening the motor circuit to arrest further movement of the brush carriage.

Although in the foregoing brief description of the invention the two terminal banks have been described as mounted verticallyon the switch frame with the switch units mounted horizontally, it will be obvious that the banks could be mounted horizontally, one above the other, with the switch units mounted vertically. It should be particularly noted that the entire frame with sixty switch units mounted thereon is very compact and occupies relatively small floor space and that due to the relatively light weight of each switch unit, the entire frame may be assembled and wired at the factory and shipped ready for installation. Furthermore, the replacement of any switch unit may be readily and speedily accomplished.

For a more complete understanding of the invention and the mode of its operation, reference may be had to the following detailed description taken in connection with the accompanying drawings of which:

Fig. 1 is a side elevational view of a switch frame embodying the invention showing a plurality of the switch units installed thereon;

Fig. 2 is a top plan view or" the switch frame;

Fig. 3 is a plan view of the normalling switch;

Fig. 4 is a sectional View of the normalling switch as viewed along section line i-Q of Fig. 3;

Fig. 5 is a partial sectional view of the nor-v malling switch as viewed along section line 5-5 of Fig. 3;

Fig.5 is a horizontal plan view of a portion of a terniinal bank, guide rod, brush carriage and associated channel member;

Fig. 7 is a vertical view of a portion of a terminal bank, brush carriage and channel member as viewed along section line l-'i of Fig. 6;

Fig. 8 shows a portion of the face of a terminal bank and contact shoes of the brush set as viewed along section line 3-8 of Fig. '7;

Fig. 9 is a partial end view of the brush carriage showing the commutator brush extensions of the brush springs; g

Fig. 10 is a side elevational view showing a portion of three switch units including the idler pulleys of two units and the brakevmagneti driving pulley and driving motor of a third unit;

Fig. 11 is an end elevational view taken along section line lI-H ofFig. 10; and

Fig. 12 is a circuit diagram illustrating the manner in which the improved switch may be used as'a line finder in a telephone system of the step-by-step type.

Referring now to the drawings, the invention will be described in more detail. Considering first Figs. 1 and 2 the switch frame comprises a base member I on one end of which are secured two channel-shaped uprights 2 and 3 joined at their upper ends by the strap 4' welded or otherwise secured thereto and joined at their lower ends by the angle bar 5 welded or otherwise secured thereto and by which the uprights are secured to the base I. Similar uprights 5 and I joined by the strap 8 and angle bar 9 are similarly mounted on the other end of base I. The upper ends of uprights 2 and 3 are also joined to the upper ends of uprights 6 and 1 by the angle bar 10 welded or otherwise secured thereto. The lower ends of uprights 2 and 3 are also suitably joined to the lower ends of uprights '6 and i by angle bar ll.

Positioned side by side between the end members of the switch frame are two panel terminal banks l2 and I3. Each bank is of the general type disclosed, for example, in Patent 1,127,741 granted February 9, 1915 to A. F. Dixon, and comprises two vertical side members i4 and I5 between which one hundred sets of multiple terminal strips and insulating separators are clamped. The banks are secured to the angle bars i0 and it by straps l8 and ll which are attached to the angle bars by screws, not shown. and to the side members l4 and Q5 of the banks by bolts l8. Each terminal strip is provided with thirty multiple terminals extending outwardly on each side of the bank, as shown in Figs. 6 and 7, and with soldering terminals at each end whereby accessibility is afforded to sixty selector switch units, thirty on each side of the bank. The terminal strips are arranged in sets of four, as most clearly disclosed in Figs. 7 and 8, to which the tip, ring, sleeve and metering leads of a subscribers line may be connected, as disclosed in Fig. 12, although in some instances, as for example where the switch frame is to be used for other purposes, each set might comprise three terminal strips. The corresponding sets of multiple terminals of the several sets of strips in both banks are aligned horizontally and individualized to diiferent selector switch units. To enable the alignment of the horizontal rows of terminal sets of one bank with the corresponding rows of terminal sets of the other bank, adjusting screws i 9 are provided which extend through the lower angle bar ii and engage beneath the side members i l and ita of the banks.

For supporting each selector switch unit on the switch frame in proper relation to the horizontal row of bank terminal sets to which it is individualized, two brackets 29 and El are provided, the supporting brackets of the switch units on the front of the frame being secured to the outside flanges of the upright channel members 2 and 6 by screws 22 and the brackets of the switch units on the rear of the frame being similarly secured to the outside flanges of the upright channel members 3 and "i. Each bracket is in general channel-shaped having a horizontal web 23, an outer flange by which it is attached to a vertical upright of the switch frame and an upwardly extending flange 2i.

Secured respectively to the flanges 24 of the brackets and 2| of each switch unit, as by screws or welding, are two L-shaped members 25 and 26 which serve to support the tubular guide rod 21 and channel member 28 of the switch unit in parallel relation to the face of the terminal banks. Each of these members is provided at its free end with two parallel inwardly extending ears 29 which together form a square socket for supporting one end of the channel member 28 which is clamped therein by a bolt 30 extending through the ends of the ears. The ends of the tubular guide rod 21 are seated in insulated bushings 3i which are secured to the members 25 and 26 in any desired manner.

Slidable on the guide rod 21 of each switch unit is a brush carriage 32 having arectangular frame 33, the'ends of which slidably embrace the guide rod. As'shown in Figs. 6, 7 and 8, which disclose the brush carriage in more detail, a channel member 34 and insulating member 35 are bolted to the front side of the frame 33 by bolts 35. To the flanges of member 34 four brush springs 31 to 40, inclusive, are secured by the screws 4 I. The brush springs are insulated from each other, from the member 34 and from the screws 4! and each is provided at one end with a contactshoe for engagement with bank terminals, as most clearly shown in Fig. 8. The brush spring 31 serves as a testing and metering brush and engages the lower edges of test terminals of the bank, brush spring 38 serves as a ring brush and engages the lower edges of the ring terminals of the bank, brush spring 39 serves as a tip brush and engages the upper edges of the tip terminals of the bank and brush 40 serves as a sleeve brush and engages the upper edges of sleeve terminals of the bank, as viewed in Figs. 7 and 8.

The inner end of each brush spring is also extended as a feeder brush, the brush extensions 42 to 45, inclusive, of brush springs 3 to 36, respectively, being vertically staggered, as shown in Figs. 7 and 9, for sliding engagement with feeder strips 46 to 49, inclusive, insulatedly secured in the inside of channel member 28. The feeder strips are each provided at one end with a soldering terminal, indicated at 50 in Fig. 2, which may be connected to terminals on the terminal block 5i secured by screws 52 to the bracket 20. By means of the feeder strips and feeder brush extensions, conductive connections may be established from the terminals on the terminal block 5! to the brush springs 37 to Aid, inclusive, irrespective of the position of the. brush carriage 32 on the guide rod 22?.

For traversing the brush carriage 32 along the guide red 2'5 a steel tape 53 is provided which runs over two pulleys or flanged drums 54 and 55 preferably made of bakelite to render them of small mass. The pulley 55 is an idler pulley andis journalled on a spindle 56 secured to the web 23 of bracket 29. Pulley 56 is a driving pulley and is similarly journalled on a spindle 51 secured to the web 23 of bracket 20. The two ends of the tape 53 are attached to the opposite ends of the brush carriage 32 by spiral springs 53 which serve the dual purpose of tensioning the tape and absorbing the shock incident to starting and stopping the brush carriage;

For driving the pulley 5G a reversible alternating current motor 59 is provided which is mounted on a lateral extension 60 of the bracket 2!] and is secured thereto by screws iii as most clearly disclosed in Figs. 10 and 11. The motor comprises a laminated stator core 62 having thereon a stator winding 63 and four shaded pole windings, 65, 66 and 61, shown more clearly in Fig. 12, and a rotor 65. The rotor shaft is journalled in two self-lubricating bearings 69 and ill attached to brass supports H and '82 which are secured to the stator core 62 by the rivets 73. Also secured to the core 52 by the rivets it are two brackets iii to which an'insulating terminal strip 115 is attached by the screws 76. binding posts to which the terminals of the pole windings at to 61, inclusive, of the motor are connected and which are in turn jumpered to terminals on the terminal block 58, as most clearly shown in Fig. 12.

The pulley 56 is driven by the motor 59 through a train of gearing comprising a gear H secured to the hub of pulley 56, an intermediate gear it journalled on a stub shaft '59 secured to the extension 8d of the bracket 29 and a pinion 85 secured to the rotor shaft of the motor. It will be noted by referring to Figs. 1, 10 and 11 that the driving motors of certain switch units are mounted at the right end thereof and that the motors of alternate units are mounted at the left end thereof for the purpose of permitting I the units to be mounted compactly on the switch frame thereby materially reducing the height of the switch frame and enabling the use of standard panel banks.

Associated with each switch unit adjacent to the driving motor 59 thereof is a magnetically controlled brake which cooperates with the tape 53. Each brake comprises an end support 82 which is secured to the free arm of the L- shaped member 25 by screws 88 which extend through the support 82 and the spacing sleeves 8d and engage in threaded openings in the member 25. Secured to the inner side of the support 82 is an L-shaped return pole-piece 85 through which and through the support 82 the magnet core 86 is threaded. The threaded end of the core is provided with a slotted end portion by means of which the core may be turned in the threaded opening in the support 82 for adjusting the air-gap between the free end of the core and the magnet armature. For clamping the core in its adjusted position the lock nut 87 is provided. A magnet coil 88 is supported on the free end of the core 86.

Secured to the free end of the pole-piece 85 by screws is an L-shaped bracket 89 provided at the end adjacent to the free end of the polepiece with ears between which the magnet armature Qii is pivoted. One end of the armature overlies the end of the pole-piece 85 and the magnet core 88 and is provided near its pivot with a brake shoe 96 which cooperates with the brake shoe 92 attached to the member 25. The coiled spring 93, one end of which is secured to the outer end of the armature 98 and the other end of which is secured to the free end of bracket as, is provided for normally retracting the armature 961 and forcing the brake shoe 9i carried thereby toward the stationary brake shoe 92 to clamp the tape 53 therebetween. The position of the brake shoe 9i with respect to the pivot point of the armature, to the point of attachment of the spring 93 to the armature and to the end of the armature which overlies the end of core 56 is so chosen that the motion of the brake shoe is very slight, in'the order of a few thousandths of an inch, but that the braking effort applied thereto by the springtS is'quite The terminal strip is provided with three large. Since, however, the end of the armature which overlies the magnet core has considerable leverage, the magnet coil ttwhen energized is quickly able to overcome the spring as to disengage the brake shoe 9| from the tape 63.

Insulatedly supported on the outer end of bracket 89 is a pair of contact springs M and 95, the inner one of which 96, is engageable by an insulating stud secured to the outer end of the armature 96 whereby when the armature is attracted to release the brake the contact springs are moved into engagement with each other for a purpose to be later described.

Each switch unit is provided with a normalling switch act mounted on the channel member 2a of the switch unit opposite the mid-point between the two banks 52 and 83. The normalling switch which is disclosed in detail in Figs. 3 to 5, inelusive, comprises a horizontal mounting plate lti secured by screws N32 to the top flange of the channel member 23, two contact pile-ups secured thereto and insulated therefrom by the hard rubber insulating strip Ed t and a switch bar pivoted to the mounting plate between the two contact pile-ups.

The left-hand contact pile-up comprises two separate bottom members m and its positioned adjacent to the insulating strip 5M and out of contact with each other, the member M35 having a soldering terminal it? and the member are having a soldering terminal 098. Superimposed on the members 585 and tilt is a hard rubber insulating strip the on the upper portion of which is superimposed the contact member iiii having the soldering terminal iii. The contact members are and Hit are arcuate in formation and extend parallelly toward the pivoted switch bar. For securing the members of the contact pile up to the support iilil bolts M2 are provided which extend through the contact members and insulating, strips ltd and its and'which are insulated from the contact members by insulating sleeves surrounding theirshanlrs and by insulating washers 8 83 inserted beneath their heads.

The right-hand contact pile-up comprises a bottom contact member lid positioned adjacent to the insulating strip ltd and having a soldering terminal H5, an insulating strip Mt superimposed thereon and two contact members it? and i is superimposed on the strip Hit, the member l'i'i having a soldering terminal iii] and the member 9 it having a soldering terminal iii]. The contact members ii and iii are arcuate in formation and extend parallelly toward the pivoted switch bar. For securing the members of the contact pile-up to the support iti, bolts H2 are provided which extend through the contact members and insulating strips its and H8 and are insulated from the contact members by insulating sleeves surrounding their shanks and by the insulating washers H3 inserted beneath their heads.

The pivoted switch bar is a composite member comprising two blades IN and H22 separated from each other by an interposed strip of insulating material. The composite switch bar is pivoted on a bolt I23 which extends through the metal sleeve i25, the mounting plate iiii, insulating strip lfl l, contact member m5, the composite switch bar, the contact member H8 and the insulating washer i25 and is held in place by the lock nuts 526. For insulating the bolt from the contact members Mid and H8 and from the blades l2! and iii, the bolt is surrounded by an insulating sleeve, as most clearly shown in Fig. 4.

ETD

Gil

As thus assembled the switch blade I 2I is in electrical contact with the contact member II8 and the blade I22 is in electrical contact with the contact member I05, good contact between them being insured by the spiral spring I21 which is interposed between the head of the bolt I23 and 121216 mounting plate IIII surrounding the sleeve I 4.

Pivoted to the outer end of the switch blade I22 are two fingers I28 and I29, the inner ends of which are normally positioned against the stop pins I30 by the coiled spring I3I, the ends of which are secured to the inner ends of the fingers. In the upper portion of Fig. 2 the switch unit brush carriage is shown in its normal position at the mid-point between the terminal banks, in which position the insulated tip of the trip finger I03 attached to the brush carriage is engaged between the fingers I28 and I29 of the switch bar of the associated normalllng switch I03 and the switch bar is thus held in its neutral position, or the position disclosed in Fig. 3.

Should the brush carriage move to the left, as viewed in Fig. 3, and engage the insulating tip of its trip finger III3 against the finger I28, due to the engagement of the finger against the stop pin Ltd, the movement of the brush carriage will rotate the switch bar about the pivot bolt I 23 thereby engaging its blades HI and I22, respectively, with the contacts IIO and I 85 whereby two circuits are established, one from soldering terminal IIl'I of contact member I05, through switch blade I22 and contact member IE3 to the soldering terminal I08 thereof, and the other from soldering terminal I20 of contact member Mil through switch blade I2I and contact member Iii to soldering terminal III. Should the brush carriage move to the right as viewed in Fig. 3, and engage the insulating tip of its trip finger I03 against the finger I23, the switch bar then will be rotated to the right thereby engaging its blades IEI and I22, respectively, with the contact members III and II l whereby two circuits are established, one from soldering terminal iii? of contact member I535 through switch blade I 22 and contact member I I l to the soldering terminal I I5 thereof and the other from soldering terminal of contact member M8 through switch blade I2I and contact member I I71 to the soldering terminal Iii) thereof. The purpose of these circuits will be apparent from the following description of the application of the invention to a typical telephone system.

For the purpose of illustrating one of the many possible uses of the selector switch hereinbefore described, the switch has been shown in Fig. 12 as a line finder in a machine switching telephone system of the well-known step-by-step type. It is to be understood, however, that it could be equally well used in any type of telephone system where line, trunk or link hunting functions are I to be performed.

Referring now to Fig. 12, two of the subscribers lines I32 and I33 of a group of two hundred lines are shown terminating, respectively, in the banks I 2 and I3 of a line finder frame. The brushes 377 to til, inclusive, associated commutator brushes 32 to 35, inclusive, commutator strips lt to 69, inclusive, reversible driving motor 59, brake magnet 88, terminal block 5| and normally switch I IIII of one of the switch units on the line finder frame, the control relays individual thereto, the control relays common to all switch units on the frame and the brushes and some of the relays of the first selector switch I90 individual to the line finder unit are also shown.

It will first be assumed that the subscriber whose line is indicated at I32 as terminating in bank I2 or the left bank of the line finder frame, initiates a call by removing the substation receiver from the switchhookthereby establishing a circuit for the line relay I35. This circuit may be traced from battery through the winding of relay I35, the right back contact of cut-off relay I36, ring conductor I3'I of the line, through the sub-station, returning over tip conductor I35 to ground at the left back contact of relay I36. Line relay I35 thereupon operates, disconnecting at its back contact the winding of the subscriber's message register I39 from the metering and testterminal I40 of the bank I2, at its right front contact connecting the terminal I40 to the winding of test relay I4I, which is common to all two hundred subscribers lines which terminate in banks I2 and I3 and, at its left contact, establishing a circuit from ground thereover, over the back contact of group relay I42, which is common to the one hundred lines including line I33 terminating in bank I3, to battery through the winding of group relay Hi3 which is common to the one hundred lines including line I32 terminating in bank I2.

Group relay I43 upon operating opens at its back contact the operating circuit of group relay Id2 to prevent any line in its one hundred line-group from. starting a line finder at this time and at its outer right contact establishes a circuit for start relay I4 3 which is individual to the line finder unit disclosed. This circuit may be traced from battery through the left winding of relay I II, the outer left back contact of start circuit relay I65, also individual to the line finder unit disclosed, outer right contact of relay M3 to ground at the right back contact of common relay I58.

Relay I M upon operating prepares an operating circuit over its left front contact through the right winding of relay I 35, at its left back contacts disconnects ground from the switch blades iii and I22 of the normalling switch I Iii at its inner right front contact prepares a locking circuit for itself, at its next-to-inner right front contact prepares a short-circuiting path for the pole windings and 66 of the motor 5%, at its middle right front contact establishes a short-circuiting path for the pole windings 65 and ti of the motor, at its nextto-outer right front contact establishes an opcrating circuit for the brake magnet 88 and at its outer right front contact establishes a loop circuit for operating the line relay I65 of the first selector switch I96. This latter circuit may be traced from battery through the right winding of relay M6, left back contact of cut-through relay IQ'I, outer right front contact of relay M l, inner right back contact of relay I lI to ground through the left winding of relay IliE. Relay I 56 operates over this circuit and establishes an obvious operating circuit for slow-to-releaserelay M8 thereby preparing the selector switch for subsequent operation and connecting ground to holding conductor I59.

Brake magnet 88 now operates in a circuit extending from battery over a terminal of terminal block 5i through its winding, a second terminal on terminal block 5|, the neXt-to-outer right front contact of relay I44 to ground at the back contact of common test relay I I-I With magnet 88 operated the brake shoe 9! is withdrawn from the tape 58 of the line finder switch unit and the stator winding 63 of the motor 59 is connected to the source of alternating current I36 over a circuit extending from the source I35, 9. terminal of terminal block 5i, stator wind! ing 53, contacts 94! and 95 closed by the energization of magnet '55, over another terminal of terminal block 5i to the source I35. Simultaneously with the operation of brake magnet I38 the short-circuiting path for pole windings and 57 is closed from ground over a terminal of terminal strip 5I, right terminal of terminal block 15, thence serially through windings 5i and 55, center terminal of strip I5; a terminal on terminal block 5i, middle right front contact of relay I64, inner right front contact of relay I59 to ground at the back contact of relay I 39.

With the stator Windlilg 53 energized by alternating current, the pole windings 65 and ti short-circuited and the pole windings 55 and 55 open-circuited,the rotor 58 of motor 59 rotates in a counter-clockwise direction and through the train of gears M, It and W, rotates the driving pulley 53 in a counter-clockwise direction whereby the tape 53 is driven in such a direction as to move the brush carriage 32 of the switch unit toward the left in a hunting movement over a horizontal row of sets of terminals of the bank I2 to which the switch unit has access.

Upon the initial movement of the brush carriage from its normal position between the two banks of terminals, the trip finger I03 carried thereby moves the switch blades I2I and I22 of the normalling switch I09 to the left in which position the blade I2! engages terminal III] and the blade I22 engages terminal I86 for a purpose to be later described. As the brush carriage advances the brushes S'I to 59, inclusive, carried thereby successively engage the sets of bank terminals of the one hundred lines including line I32 which appear in the left bank I2.

For arresting the movement of the brush carriage when the test brush 31 thereof encounters the test terminal of a calling line, the fast operating test relay MI is providedwhosewinding is norcally connected in a series circuit from battery through the one thousand ohm resistance I59,

the one hundred ohm resistance I5I and a first condenser I52 to ground, the resistance I59 beingshuntedby a second condenser I53. Condensers I52 and I53; are thus normally fully charged over this circuit. When now in the advance of the brush carriage the test brush 31 engages the test terminal I50 of the calling line to which the winding of the test relay I lI has been connected, as previously described, a circult is established from ground at the left front contact of relay I48 over holding conductor I69, right back contact of relay I 35, resistance I58, a terminal on terminal block 5I which is a portion of terminal block 5I, feeder strip 56, feeder brush 52, test brush 3?, test terminal Hill, right front contact of relay I35, resistance I59 and winding of relay MI to battery. Relay I II will tend to operate over this circuit, but does not have time to fully operate as the brush carriage is then travelling at high speed and the test brush S'l will overrun the test terminal I69 and make a passing contact therewith for only a small fraction of a second. This time is not sufiicient to operate relay MI for releasing the brake magnet 58 and for stopping the brush set on the calling line terminal set. Condensers I52 and I53 and resistances I55 and I5I are therea brush on the test terminal.

When therefore the test brush 91 momentarily engages the test terminal, a. discharge path for condenser I53 is established from ground through resistance I59 applied over thetest brush, thence through resistance I5I and condenser I52 to ground over which path condenser I52 discharges sumciently so that when the test brush overruns and leaves the test terminal llli suficient current will flow from battery through the winding of relay IIlI, condenser I53 which is now charged and offers a low resistance, resistance I5I and condenser I52 to ground to cause the operation of test relay'llil. Relay l il will now remain operated until condenser I52 becomes fully charged at which time, due to the decay of the charging current, relay IlI will release.

As soon as relay I il operates it opens at its back contact the operating circuit or brake magnet M which releases clamping the moving tape 53 of the finder switch unit between the brake shoes 9! and 92 to immediately arrest the movement of the tape. Magnet 98 is made slightly slow to release at this time by the removal of the shunt from the circuit extending through resistance IGI, condenser I62, back contact of relay I63 and the back contact of relay I59 to ground. Brake magnet 88 upon releasing also disconnects the source of alternating current Itfi from the stator winding 63 of the motor.

At substantially the same instant the energi zation of test relay MI reestablishes an operatand the winding of relay I49 to battery. Relay I59 upon operating opens at its back contact the short-circuit path through the pole windings t5 and 67 and locks itself in a circuit extending from battery through its winding, resistance I5 5 and'its own left contact, winding of relay I59 to ground at the left back contact of relay I69. Relay I59 does not, however, operate in this locking circuit since its winding is shunted by ground applied over the front contact of test relay I lI so long as relay It! remains operated.

To insure that relay M9 will operate and look even though its operating circuit is momentarily opened due to the vibration of the front contact of test relay I II, resistances I59 and I55 and condensers I56 and I5? are provided, the condensers being normally charged over a path extending from battery through the winding of relay I59, condenser I57, resistance I55, condenser I55 to ground. Should the front contact of relay ItI chatter upon closing, a momentary closure thereof while of insufficient duration to cause relay I59 to operate and lock, will cause condenser I56 to discharge sufiiciently over the discharge path traced from ground over the front contactof relay I M, through resistance I55 and condenser I56 to ground so that if the front contact of relay I II should then momentarily open due to chatter, sufiicient current will flow from battery through the winding of relay I59, condenser I51 which is now charged and offers a low resistance, resistance I55 and condenser I5;6 to ground to cause the operation of ground over a terminal of terminal block 5|,

right terminal of terminal strip I5 thence serially through windings B4 and 66, left terminal of strip I5, a terminal of block 5I, next-to-,

inner right contact of relay I44, middle right front contact of relay I 43 through resistance I72 to ground at the right front contact of relay H9. Upon the release of test relay MI, as previously described, ground is removed from the operating circuit of relay MS and one terminal of the winding of relay I59 and relay l59 now operates in the locking circuit of relay M9 in turn establishing an obvious operating circuit for slowto-release relay 863. At its back contact relay Hi again establishes the previously traced operating circuit for brake magnet 88. With brake magnet 33 operated the brake shoe 9| is released from the tape 53 and the stator winding 63 of the motor 59 is connected to the alternating current source i3 3.

With the stator winding 63 now energized, the pole windings f t and 6t short-circuited through resistance W2 and the pole windings 65 and Si open-circuited, the rotor 68 of the motor 59 rotates at a slower speed in a clockwise direction thus rotating the driving pulley 5 in the same direction to advance the brush carriage iii. towards the right until the test brush 3'? again engages the test terminal Mil of the calling line, at which time, since the brush carriage does not now attain a high speed, an operating circuit for test relay t lt is established, This circuit may be traced from ground applied to the test brush Ell through resistance loll, thence over test terminal M6, condenser i523 which "oeing fully charged offers a low resistance to the flow of current in parallel with resistance ltlil, winding of relay t ll to battery. Relay l li now operates to open the circuit of brake magnet 88 since with relay I153 operated the circuit through resistance tilt and condenser i6?) is ineffective magnet releases q'iiclzly to arrest the movement of the brush carriage with the brushes thereof in entely releases and opens the Before slow-to-release relay has nine to release, with relay 559 released an operating circuit is established for relay H38 which he ced from ground the back contact of relay l5 front contact of relay Hi3, winding of relay iinier right front contact and right winding f relay 1W1 to battery. Relay lull now operates, opening at right back contact the initial operating circuit of relay l ll, opening at its left back contact the locking circuit of relay which, however, is now maintained operated under the control of relay Ml, and at its right front contact establishes the operating circuit of start circuit relay M5. The circuit of relay M5 may he traced from battery. through its right winding, the outer left front contact of relay M4 to ground at the right front contact of relay I56. Relay 6515 upon operating locks in a circuit from ground at the left front contact of relay I48 over holding conductor ltd, its next-to-inner and inner right front contacts and right winding to battery. When relay H53 finally releases after a predetermined interval following the release of relay i59, the circuit through the winding of relay I60 circuit and the locking winding of relay I is opened and relays I60 and I now both release since the initial operating circuit of relay I has been opened through the operation of relay I45. With relay I 44 now released the short-circuiting path through the pole windings 54 and 66 of the motor 59 is opened.

With start circuit relay 5 operated the tip conductor I38 of the calling line is extended over tip terminal I64, tip brush 39, feeder brush M, feeder strip 43, terminal of terminal block 5|, outer right front contact of relay 5, left back contact of cut-through relay I47 to battery through the right winding of relay M6 and the ring conductor i3l of the calling line is extended over ring terminal E65, ring brush 38, feeder brush d3, feeder strip 41, a terminal of terminal block 5!, next-to-outer right front contact of relay I 45, inner right back contact of relay M1 .to ground through the left winding of relay I46.

Relay 846, whose initial operating circuit was previously established over the outer right front contact of relay M4, is now maintained operated over the calling line loop thus maintaining relay N8 operated. The operation of relay M5 also establishes a circuit for cut-off relay H36 of the calling" line which may be traced from ground at the left front contact of relay Mil, ductor 3239, the next-to-inner of relay 5 35, a terminal of feeder strip til, feeder brush to, sleeve brush 419, sleeve terminal EGG, winding of relay 636 to battery. This same ground is also applied to the test multiples it?! of the calling line appearing in the banks of all connector switches having access to the line to maria the line busy to such connector switches. Relay M5 at its outer left front contact also extends the start wire extending from the contacts of group relays 9G2 and M3 so that if any other line in the two hundred linegroup of subscribers lines is calling the start relay of another available line finder unit, corresponding to relay may be operated to start such other line finder unit. At its right loaclr contact relay l lo also opens the circuit of test relay Ml which releases and in turn releases relay i l-l.

The cut -off relay upon operating disconnects the winding of line relay 53 5 from the over holding conright front contact terminal block 59',

calling line whereupon relay ldti releases reconmagnet to the necting the message register terminal l lo, opening at its right front contact a second point in the operating circuit of relay l ll and at its left contact opening the operating circuit of group relay @5 3 which will now release if no other line in the same one hundred linegroup of lines in which the calling line is located, is at the time in a calling condition. The common con rol relays i l-i, Mil, its and H53 are now released in readiness to control another line finder switch unit for establishing a connection with another calling line.

The calling line being now operatively connected with the first selector switch tell, the calling subscriber may proceed to operate his substation dial to set up a connection to a desired subscribers line, out-through relay t ll operating in the usual manner after the operation of the selector switch iii-l to out the talking circuit through to the succeeding selector switch and to disconnect the winding of relay M5 which thereupon releases in turn releasing relay M8. Holding ground for relay M5 and for maintaining cut-off relay H operated is thereafter supplied in the usual manner from the succeeding selector switch over a front contact of cutemployed in establishing the connection are restored in the usual manner and holding ground is removed from conductor sec thereby releasing cut-off relay I36 of the calling line and releasing relay Hit. With both relays its and M4 released,

ground is connected over the back contacts there-,

of to switch blades 52! and 522 of the normalling switch I86. It will be recalled that the blades of this switch were moved to the left by the movement of the brush carriage 32 to the left. Therefore, a circuit is now established from ground over the middle left back contact of relay 55, the outer left back contact of relay Mid, a terminal on terminal block 5!, switch blade it i contact terminal Md, terminal of terminal block 5|, the left terminal of terminal strip l5, thence serially through pole windings $6 and d6 of motor '59, right terminal of strip 35 and a terminal of block 5! to ground thus short-circuiting these windings. A second circuit is also established from ground over'the inner left back contact of relay Hi5, inner left back contact of relay Hi l, a terminal on terminal block 5!, switch blade I22, contact terminal Hit, a terminal on terminal block 5|, winding of brake magnet 88,

a terminal on terminal block 5! to battery. Magnet 88 now operates releasing the brake shoe at from the tape 53 and closing the circuit of stator winding 63 of motor 59.

The rotor 68 of the motor now rotates in a clockwise direction thereby moving the brush carriage to the right. When the trip finger its engages the finger E28 carried by the switch bar N2 of the normalling switch, it rotates it away from the associated stop pin iSii against the tension of spring lei and snaps over it into engagement with the finger i29 and since the finger H9 is prevented from pivoting by its associated stop pin l3t the switch blades l2! and I22 are moved by the continued movement of the brush carriage into their neutral position. As soon as the switch blades become disengaged from the contact terminals iii! and "it the circuit of magnet 88 is opened and the short circuit of the pole windings 6E and fi iis also opened thereby arresting the further movement of the brush carriage. The brush carriage is now in its normal position midway between the two terminal banks, as disclosed in Fig. 2.

It will now be assumed that the subscriber whose line i3? is disclosed as terminating in the right terminal bank l3 initiates a call thereby operating line relay Hi3 to mark the test terminal Ill with calling potential and to operate the group relay M2. The circuit of relay Hi2 may be traced from ground at the left contact of relay H0, back contact of group relay M3, winding of group relay N32 to battery. In response to the operation of group relay Hi2, relay we is operated in the manner previously described and an operating circuit for the brake magnet 88 and a short-circuiting path for the pole windings 64 and 6d are established thereby. The operating circuit for magnet 88 is the same aiaaaae as previously traced and the short-circuiting path for windings 66 and 66 extends from ground over a terminal on terminal block 5|, the right terminal on strip 75, thence serially through windings 6d and 66, left terminal on strip 15,. a terminal on block 5!, nex't-to-inner right front contact of relay Mt, middle right front contact of relay, H 32 to ground at the back contact of relay M9.

Upon the energization of magnet 88 thebrake shoe is released from the tape 53 and the circult of the stator winding 63 of the motor 59 is closed and with the pole windings 6d and 65 short-circuited and the pole windings t5 and 6? open-circuited, the rotor 68 of the motor is rotated in a clockwise direction thusmoving the brush carriage 32 to the right for hunting in the right terminal bank It. The initial movement of the brush carriage now moves the blades i2! and 522. of the normalling switch Hill to the right into engagement respectively with contact terminals M7! and lid. The circuits now function in the manner previously described except that the test relay MS is now controlled to stop and center the brushes 3? to 69, inclusive, on the terminal set of the'calling line its due to the engagement of the test brush 3'! with the test terminal Hi. In

this case, however, in the event that the brushes overrun the terminal set, the operation of relay 859 causes the short-circuiting of the pole windings $5 and El of the motor to rotate its rotor counter-clockwise thereby driving the brush carriage back to the terminal set. The path over which the windings 65 and 5? are short-circuited may be traced from ground over a terminal of terminal block 5%, right terminal of strip 15, thence in series through windings El and B5, centerterminal of strip 15, a terminal of block 5!, middle right front contact of relay i 34, inner right front contact of relay M2, resistance I12 to ground at the right front contact of relay its.

Whenground is removed from holding conduc-' tor 69 upon the termination of the connection and relay I65 releases, with relay Hi l at that time released and the switch blades l2! and I22 in their right operated positions, a circuit is established for brake magnet 88 extending from ground over the inner left back contacts of relays M5 and ldd, a terminal of terminal block 5|, switch blade E22, contact terminal I It, a terminal of block 5!, winding of magnet 88, a terminal of block 55 to battery. Magnet 88 operates releasing the brake shoe 9! from the tape 53 and closing the energizing circuit of the stator winding 63 of I the motor. A short-circuiting path for the pole windings 65 and El is also established from ground over the middle left back contact of relay I45, the outer left back contact of relay Hi l, a terminal on terminal block 5|, switch blade I25, contact terminal ill, a terminal on terminal block 5!, the center terminal on strip 15, thence serially through pole windings 65 and El, the right terminal on strip 15 and a terminal on block 5i to across said bank, means for driving said belt, and yielding means for attaching said brush carriage to said belt.

2. In a selector switch having a bank of terminals and a brush set cooperating therewith, a brush carriage upon which said brush set is mounted, a belt for traversing said brush carriage across said bank, supporting pulleys for said belt, means for driving said belt, and coiled springs by which each end of said belt is attached to said brush carriage for tensio-ning said belt.

3. In a selector switch having a bank of terminals and a brush set cooperating therewith, a brush carriage upon which said brush set is mounted, a guide rod positioned parallel to the face of said bank upon which said brush carriage is slidable, a channel bar positioned parallel to said guide rod, a plurality of feeder strips positioned within said bar and insulated therefrom and from each other, and feeder brush extensions of the brushes of said brush set engaging with said feeder strips.

4. In a selector switch having a bank of terminals and a brush set cooperating therewith, a brush carriage upon which said brush set is mounted, a belt for traversing said brush car riage across said bank, supporting pulleys for said belt, means for driving said belt, coiled springs by which each end of said belt is attached to said brush carriage, and a magnet operated brake for arresting the movement of said belt, said springs serving to tension said belt and to absorb the kinetic energy of said brush carriage and brush set when the movement or" said belt is arrested.

5. In a selector switch having a bank of terminals and a brush set cooperating therewith, a brush carriage upon which said brush set is mounted, a belt for traversing said brush carriage across said bank, supporting pulleys for said belt, means for driving said belt, and a brake for arresting the movement of said belt, said brake comprising a fixed and a movable brake shoe positioned respectively on opposite sides of a traverse of said belt, an electromagnet having an armature on which said movable brake shoe is supported, and a spring for holding said armature normally retracted whereby said belt is clamped between said brake shoes.

6. In a selector switch, a supporting frame having end members, two panel banks of terminals supported on said frame, and a switching unit for cooperation with said banks of terminals comprising end brackets for attachment to said frame members, a guide rod and a supporting bar joining said brackets, a brush carriage normally positioned opposite the mid-point between said banks and slidable on said guide rod and carrying a single set of brushes, a belt for traversing said carriage in either direction along said guide rod, an idler pulley journalled on one of said brackets and a driving pulley journalled on the other of said brackets over which said belt runs, and a reversible alternating current motor mounted on the last named bracket and gearedto said driving pulley for driving said belt.

7. In a selector switch, a supporting frame having end uprights, two panel banks of terminals supported on said frame and a switching unit for cooperation with said banks of terminals comprising end brackets for attachment to said frame uprights, a guide rod and a supporting bar joining said brackets, a brush carriage normally positioned opposite the mid-point between said' banks and slidable on said guide rod, a single set of brushes and a trip finger mounted on said carriage, a belt for traversing said carriage in either direction along said guide rod, an idler pulley journalled on one of said brackets and a driving pulley journalled on the other of said brackets over which said belt runs, a reversible motor mounted on the last named bracket and geared to said driving pulley for driving said belt, and a normalling switch mounted on said supporting bar at the mid-point thereof and operable by the trip finger on said brush carriage to control said motor to return said brush carriage to its normal position.

8. In a selector switch, a supporting frame having end uprights, two panel banks of terminals supported on said frame and a switching unit for cooperation with said banks of terminals comprising end brackets for attachment to said frame uprights, a guide rod and a supporting bar joining said brackets, a brush carriage normally positioned opposite the mid-point between said bank and slidable on said guide rod, a single set of brushes and a trip finger mounted on said carriage, a belt for traversing said carriage in either direction along said guide rod, an idler pulley journalled on one of said brackets and a driving pulley journalled on the other of said brackets over which said belt runs, a reversible motor mounted on the last named bracket and geared to said driving pulley for driving said belt, a magnet controlled brake cooperating with said belt secured to said last named bracket adjacent to said motor, and a normalling switch mounted on said supporting bar at the mid-point thereof and operable by the trip finger on said brush carriage to control said brake and said motor to return said brush carriage to its normal position.

9. In a telephone system, a selector switch having a panel bank of terminals and a brush set cooperating therewith, a belt for traversing said brush set across said bank, a reversible alternating current motor for driving said belt, said motor having a stator winding and two pairs of normally open-circuited shaded pole windings, means eifective when a terminal of said bank is marked as in a calling condition for causing the energization of said stator winding and the short-circuiting of one pair of said pole windings whereby said motor is operated in a direction to traverse said brush set in a hunting movement over said bank, testing means for arresting the hunting movement of said brush set when it engages said marked terminal, and means operated by said testing means for open-circuiting said short-circuited pole windings and for short-cireuiting said other pole windings whereby said motor is re versed to return said brush set to said marked terminal when said brush set overruns said terminal in its hunting movement.

10. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, a belt for traversing said brush set across said banks, a reversible alternating current motor for driving said belt, said motor having a stator winding and two pairs of normally open-circuited shaded pole windings, means operative in accordance with the bank in which a marked terminal is located for causing the energization of said stator winding and the short-circuiting of one pair of pole windings whereby said motor is operated in a direction to traverse said brush set' in a hunting movement over the bank in which the marked terminal is located, arid testing means for arresting the hunting movement of said brush set when it engages said marked terminal.

11. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, a belt for traversing said brush set across said banks, a reversible alternating current motor for driving said belt, said motor having a stator winding and two pairs of normally open-circuited shaded pole windings, means operative in accordance with the bank in which a marked terminal is located for causing the energization of said stator winding and the short-circuiting of one pair of pole windings whereby said motor is operated in a direction to traverse said brush set in a hunting movement over the bank in which the marked terminal is located, testing means for arresting the hunting movement of said brush set when it engages said marked terminal, and means operated by said testing means for open-circuiting said short-circuited pole windings and for short-circuiting said other pole windings whereby said motor is reversed to return said brush set to said marked terminal when said brush set overruns said terminal in its hunting movement.

12. In a telephone system, a selector switch having a panel bank of terminals and a brush set cooperating therewith, a reversible alternating current motor for advancing said brush set over said bank, said motor having a stator winding and two pairs of normally open-circuited shaded pole windings, means efiective when a terminal of said bank is marked as in a calling condition for causing the energization of said stator winding and the short-circuiting of one pair of said pole windings whereby said motor is operated in a direction to advance said brush set in a hunting movement over said bank, testing means for arresting the hunting movement of said brush set when it engages said marked terminal, an ofi-normal switch controlled by the movement of said brush set from its normal position, and means including said ofinormal switch for causing the energization of said stator winding and the short-circuiting of the other pair of said pole windings whereby said motor is operated in the reverse direction to return said brush set to its normal position.

13. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, a reversible alternating current motor for advancing said brush set over either of said banks, said motor having a stator winding and two pairs of normally opencircuited shaded pole windings, means operative in accordance with the bank in which a marked terminal is located for causing the energization of said stator winding and the short-circuiting of one pair of said pole windings whereby said motor is operated in a direction to advance said brush set in a hunting movement over the bank in which the marked terminal is located, testing means for arresting the hunting movement of said brush set when it engages a marked terminal in either bank, a normalling switch controlled by the movement of said brush set in either direction from its normal position, and means including said normalling switch for causing the energization of said stator winding and the short-circuiting of the other pair of said pole windings whereby said motor is operated in the reverse direction to return said brush set to its normal position.

14. In a telephone system, a selector switch having a panel bank of terminals and a brush set cooperating therewith, a belt for traversing said brush set over said bank, a reversible alternating current motor for driving said belt, said motor having a stator winding and two pairs of normally open-circuited shaded pole windings, a brake for normally holding said belt against movement, a magnet operable to release said brake and to cause the energization of said stator winding, means effective when a terminal of said bank is marked as in a calling condition for causing the energization of said magnet and the shortcircuiting of one pair of said pole windings whereby said motor is operated in a direction to advance said brush set in a hunting movement over said bank, testing means operative when said brush set engages said marked terminal to release said magnet to apply said brake and to deenergize said stator winding whereby the hunting movement of said brush set is arrested, and means eiiective when said brush set overruns said marked terminal to reoperate said magnet, reenergize said stator winding, open-circuit said short-circuited pole windings and to short-circuit said other pole windings whereby said motor is operated in the reverse direction to return said brush set to said marked terminal.

15. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith and normally positioned midway between said banks, a belt for traversing said brush set over said banks, a reversible alternating current motor for driving said belt, said motor having a stator winding and two pairs of normally open-circuited shadedpole windings, a brake for normally holding said belt against movement, a magnet operable to release said brake and to cause the energization of said stator winding, means operable in accordance with the bank in which a marked terminal is located for causing the energization of said magnet and the short-circuiting of one pair of said pole windings whereby said motor is operated in a direction to advance said brush set in a hunting movement over the bank in which the marked terminal is located, testing means operative when said brush set engages said markedterminal to release said magnet to apply said brake and to deenergize said motor whereby the hunting movement of said brush set is arrested, and means effective when said brush set overruns said marked terminal to reoperate said magnet, reenergize said stator winding and to short-circuit said other pole winding whereby said motor is operated in the reverse direction to return said brush set to said marked terminal.

16. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith and normally positioned midway between said banks, a belt for traversing said brush set over said banks, a reversible alternating current motor for driving said belt, said motor having a stator winding and two pairs of normally open-circuited shaded pole windings, a brake for normally holding said belt against movement, a magnet operable to release said brake and to cause the energization of said stator winding, means operable in accordance with the bank in which a marked terminal is 10- cated for causing the energization of said magnet said brush set engages said marked terminal to release said magnet to apply said brake and to deenergize said motor whereby the hunting movement of said brush set is arrested, a normailing switch controlled by the movement of said brush set in either direction from its normal position, and means including said normalling switch for operating said brake magnet and for short-circuiting the other pair of said pole windings whereby said motor is operated in the reverse direction to return said brush set to its normal position.

17. In a telephone system, a selector switch having a panel bank of terminals and a brush set cooperating therewith, a belt for traversing said brush set across said bank, a reversible alternating current motor for driving said belt, said motor having a stator winding and two pairs of normally open-circuited shaded pole windings, means eiiective when a terminal of said bank is marked as in a calling condition for causing the energizetion of said stator winding and the short-circuiting of one pair of said pole windings whereby said motor is operated in a direction to traverse said brush set in a hunting movement over said bank, testing means for arresting the hunting movement of said brush set when it engages said marked terminal, and means operated by said testing means for open-circuiting said short-circuited pole windings and for short-circuiting said other pole windings through a resistance whereby said motor is operated at a slower speed in the reverse direction to return said brush set to said marked terminal when said brush set overruns said terminal in its hunting element.

18. In a telephone system, a selector switch having a panel bank of terminals and a brush set cooperating therewith, a belt for traversing said brush set over said bank, a reversible alternating current motor for driving said belt, said motor having a stator winding and two pairs of normally open-circuited shaded pole windings, a brake for normally holding said belt against movement, a magnet operable to release said brake and to cause the energization of said stator winding, means efiective when a terminal of said bank is marked as in a calling condition for causing the energization of said magnet and the short-circuiting of one pair of said pole windings whereby said motor is operated in a direction to advance said brush set in a hunting movement over said bank, testing means operative when said brush set engages said marked terminal to release said magnet after a predetermined interval to apply said brake and to deenergize said stator winding whereby the hunting movement of said brush set is arrested, means efiective when said brush set overruns said marked terminal to reoperate said magnet, reenergize said stator winding, opencircuit said short-circuited pole windings and to short-circuit said other pole windings whereby said motor is operated in the reverse direction to return said brush set to said marked terminal, and means effective upon the reoperation of said testing means when said brush set re-engages said marked terminal to quickly release said brake magnet to arrest the'return movement of said brush set.

WARREN W. CARPENTER. RUDOLPH F. MALLINA. 

